Field of the Invention
This invention relates, in general, to sewing devices and, in particular, to a new and useful apparatus and method for positioning and holding a thread chain for sewing it onto successively fed workpieces.
The known apparatus (U.S. Pat. No. 3,356,054) comprises an L-shaped suction tube which is arranged above the sewing machine for rotation about the mount of a suction line and communicates with the suction line and which has a suction aperture in the region of the lower end. The suction tube is rotatable between a catch position behind the needle and delivery position in front of the needle, so as to suck up the free thread chain formed behind the sewn workpiece and severed from the workpiece and to move it in a rotary movement into the delivery position in front of the needle and to hold it there so that the thread chain is bound into the seam to be formed at the next workpiece.
In this known apparatus, the suction tube describes an arc of a relatively large radius and therefore is usable only where the space to the left of the needle above the stitch plate is free. This space can therefore not be utilized for the arrangement of attachments.
When being bound into the new seam, the thread chain must be held under a certain tensile stress. However, with suction air alone a sufficiently great holding force is not attainable.
From U.S. Pat. No. 4,149,478 an overcast sewing machine is known, on which in spaced relation workpieces are fed in a transport direction and sewn, the thread chain being continued to be sewn a distance beyond the terminal edge of the first workpiece. Laterally of the seam line, a suction tube with a cutter for the thread chain is arranged after the needle. The thread chain is sucked into the suction tube and severed next to the end edge of the workpiece. Before the cutter, a blow nozzle is provided. The part of the thread chain which, having been cut by the blade, leads to the needle and is blown by the air stream issuing from the nozzle, counter to the transport direction. It is blown in front of the needle under a lifted clamping arm and is sucked into a suction tube disposed next to the clamping arm. Then the thread chain is pressed by the clamping arm against the cloth bearing surface. As the next following workpiece which is guided over the clamping arm is being supplied and sewn, the thread chain to be bound into the new seam is pulled out from under the clamping arm and sewn into the new seam.
The arrangement has the disadvantage that, at the end of the workpiece sewn first, a thread chain piece protrudes over the rear edge and must be removed by hand. In addition, due to the ejection of air in the direction of the seam line, a controlled introduction of the thread chain to be sewn into the following workpiece under the clamping arm is not always measured even with the aid of the suction, so that the thread chain is not properly aligned. The chain remains unclamped, and is not held taut, so that thread chain remainders may hang from the newly formed seam. As the use of an apparatus for positioning and holding a thread chain is automated, sewing systems presupposes faultless operation of the apparatus, this known apparatus is not suitable for automated sewing systems.